Abstract
Abstract The formation of H 2 CO in the partial oxidation reaction of CH 2 species and the adsorption of H 2 CO on clean and iodine covered Pd(1 0 0) were investigated by means of temperature-programmed desorption (TPD) and photoelectron spectroscopy (UPS). Adsorbed CH 2 was produced by thermal dissociation of CH 2 I 2 . Besides the stabilization of parent molecules by coadsorbed oxygen, the CH 2 fragments selectively oxidized by preadsorbed oxygen to H 2 CO in a reaction-limited process. The amount of formaldehyde saturates at θ O =0.2, while the total oxidation products (CO 2 , H 2 O) monotonously increased with the increase of θ O . In separate experiments the surface chemistry of H 2 CO was investigated on clean and iodine covered surfaces. The decomposition of H 2 CO was blocked by preadsorbed I. These feature is interpreted by site blocking, by weakening of the H 2 CO-Pd bond and by decreasing the bond energy between Pd and O by 50 KJ/mol. The results suggest that the electronegative additives promote the selective oxidation of CH 2 species on Pd(1 0 0) surface.
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